HVAC systems should be capable of operating efficiently under a wide range of outdoor temperatures. Current HVAC systems control outdoor (condenser) fan and indoor blower speed based on the cooling required to be provided by the system. In many such systems, outdoor fan speed is controlled such that refrigerant pressure remains within a desired range. Excessive pressure risks refrigerant leakage, and inadequate pressure risks compressor damage or failure. Subject to maintaining pressure within a desired range, the system as a whole is then controlled to operate as efficiently as possible. Some HVAC systems employ multistage compressors and multiple outdoor fans to increase operating efficiency.